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Old December 10th, 2017, 02:22 PM   #1

kalabdel is offline
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What is the start of a new electrical schematic?

Hello everyone,

I'm quite lacking in engineering practices and as I was thinking of ways to improve my AutoCAD electrical skills I realized I have no idea how to design a schematic. I usually work with existing equipment and at most add to or modify parts of it and start be hand drawing a ladder schematic then eventually draw it in Autocad to print and attach to the equipment.

How does the whole process start for a new equipment, what information do you work with start a new project?

-How do you divide the circuit, by function high voltage, low voltage, motors, sensors or by process, loading, sorting, stacking?
-A description of the machine and what it should do?
-A list of the devices used?
-If PLC is used, a list of I/Os?
-Electrical specifications, as to voltage and current?
-How much do you include in one drawing and, how much is too much and how little is too little? ( I assume it will be similar to HMI design where clarity/consistency and ease of following the drawing is of highest priority)

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Old December 10th, 2017, 04:33 PM   #2
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For me the first thing is getting written down every operational aspect of the machine, what happens before something else happens, safety's, sensors, controls needed, power requirements, etc., etc.

Then I write the schematic, and many revisions, (along with PLC & HMI programs) on paper until I am mostly done. Then I start putting it in CAD and writing the actual PLC program.

Just know beforehand that nothing is finalized until the machine is commissioned - even after years of designing panels and programming PLC's I make changes to the schematic and programs until it is built, and sometimes while commissioning.
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Old December 10th, 2017, 04:45 PM   #3
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Read the spec, sort out motor sizes, motor circuit breaker sizes, contactor sizes, MCCB size and all other bits like circuit breakers, power supplies and the like then draw the power circuit.
Next make a list of inputs and outputs, draw up the PLC and control circuit.
Manufacture the board.
Writing software eventually I just do my I/O list and write the software - no plans - it just flows - been doing it a long time. Rough and ready but works for me.
The Old Pfhaart

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Old December 10th, 2017, 08:14 PM   #4

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your example arrangement,
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Old December 11th, 2017, 03:19 AM   #5
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We arrange the schematics in this order:

Overview of functions.
Overview of locations.

Main power supply entry.
Main power bus-bar.
400V/230V control power via transformer.
230V distribution to various potentials.
400VAC to DC power supply.
DC distribution to various potentials.
Common safety (E-stops and associated safety relays).
Safety interfacing to external machines or customer areas.
Common networking (Ethernet switches and routers) (here a network overview diagram is inserted, even though the networking is already defined by each item and cable spread out in the schematics).
Common operating elements (E-stop reset, manual/auto switchover).
Interface signals to other machines (not safety relevant).

(specific functions on the machine or in the plant)
One-by-one, function by function:
Motor starters.
Safety elements that are only relevant for one function or item.
See my profile interests for Q&A
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Old December 11th, 2017, 11:00 AM   #6

kalabdel is offline
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Thanks guys, much appreciated.

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